CVE-2026-64088: batman-adv: tt: fix negative tt_buff_len

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

batman-adv: tt: fix negative tt_buff_len

batadv_orig_node::tt_buff_len was declared as s16, but the field is never
intended to hold a negative value. When a value greater than 32767 is
assigned, it wraps to a negative signed integer.

In batadv_send_other_tt_response(), tt_buff_len is temporarily widened to
s32. The incorrectly negative s16 value propagates into the s32, causing
batadv_tt_prepare_tvlv_global_data() to allocate a full sized buffer but
populates only a small portion of it with the collected changeset. All
remaining bits are kept uninitialized.

Using an u16 avoids this type confusion and ensures that no (negative) sign
extension is performed in batadv_send_other_tt_response().

The Linux kernel CVE team has assigned CVE-2026-64088 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 5.10.258 with commit 4c4c2f340f4c27373bfcac8dc5032ce7bb474e47
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 5.15.209 with commit 33e5ede7ce6d92e531920d4bbd6d3e18ef1c6430
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 6.1.175 with commit 3c96dff00998314983b68a3e7caac07a66ebe496
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 6.6.142 with commit 32edd2a28e112064020a2f319a8cb8a9e5a09767
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 6.12.92 with commit 4dab98961426d0cf6a1599cda6950b7596ca2fcd
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 6.18.34 with commit 730de8733dd90f70d7580a9b329b971f8e1474a2
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 7.0.11 with commit ed28ead3420c373a7928622f114bc6168075d1e1
	Issue introduced in 3.1 with commit a73105b8d4c765d9ebfb664d0a66802127d8e4c7 and fixed in 7.1 with commit b64963a2ceeb7529310b6cf253a1e540784422f4

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64088
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/batman-adv/types.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/4c4c2f340f4c27373bfcac8dc5032ce7bb474e47
	https://git.kernel.org/stable/c/33e5ede7ce6d92e531920d4bbd6d3e18ef1c6430
	https://git.kernel.org/stable/c/3c96dff00998314983b68a3e7caac07a66ebe496
	https://git.kernel.org/stable/c/32edd2a28e112064020a2f319a8cb8a9e5a09767
	https://git.kernel.org/stable/c/4dab98961426d0cf6a1599cda6950b7596ca2fcd
	https://git.kernel.org/stable/c/730de8733dd90f70d7580a9b329b971f8e1474a2
	https://git.kernel.org/stable/c/ed28ead3420c373a7928622f114bc6168075d1e1
	https://git.kernel.org/stable/c/b64963a2ceeb7529310b6cf253a1e540784422f4